1. Field of the Invention
This invention relates to wireless communications systems, and more particularly, to closed loop power control techniques for use in wireless communications systems.
2. Description of the Related Art
(Note: This application references a number of different publications as indicated throughout the specification by reference numbers enclosed in brackets, e.g., [x]. A list of these different publications ordered according to these reference numbers can be found below in Section X of the specification. Each of these publications is incorporated by reference herein.)
Power control is often necessary in wireless communications systems. For example, a DS-CDMA (direct sequence—code division multiple access) wireless communications systems must implement power control, because all users share the same bandwidth to transmit data and interference among users often occurs. Generally, the signal received by a base station (BS) from a nearby mobile station (MS) will dominate that received from a far MS.
The objective of power control is to control the transmission power of the MS such that the average received power from each MS is constant. Power control reduces inter-user interference by overcoming the near-far effect and results in capacity increase of the overall CDMA system. Power control also combats the Rayleigh fading channel effect on the transmitted signal by compensating for the fast fading of the wireless channel. Finally, power control minimizes the power consumption of the MS.
Power control can be classified into two main categories, namely, open loop and closed loop power control. In Open Loop Power Control (OLPC), the MS measures the quality of the signal received from the BS and adjusts its transmission power accordingly. In Closed Loop Power Control (CLPC), the BS measures the fading effects in the signal received from each MS, and then commands each MS to increase or decrease its power accordingly.
Notwithstanding these accomplishments, there remains a need in the art for improved methods of power control.